Nearby galaxy is a ‘fossil’ from the early universe

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Scientists analyzed the chemical elements in the faintest known galaxy, called Segue 1, and determined that it is effectively a fossil galaxy left over from the early universe. Stars form from gas clouds and their composition mirrors the chemical composition of the galactic gas from which they were born.

New work from a team of scientists including Carnegie's Josh Simon analyzed the chemical elements in the faintest known galaxy, called Segue 1, and determined that it is effectively a fossil galaxy left over from the early universe.

Astronomers hoping to learn about the first stages of galaxy formation after the Big Bang use the chemical composition of stars to help them unravel the histories of the Milky Way and other nearby galaxies. Using these chemical analysis techniques, the team was able to categorize Segue 1's uniquely ancient composition. Their work is published by Astrophysical Journal.

Stars form from gas clouds and their composition mirrors the chemical composition of the galactic gas from which they were born. Only a few million years after stars begin burning, the most-massive stars explode in titanic blasts called supernovae. These explosions seed the nearby gas with heavy elements produced by the stars during their lifetimes. The very oldest stars consist almost entirely of the two lightest elements, hydrogen and helium, because they were born before ancient supernova explosions built up significant amounts of heavier elements.

In most galaxies, this process is cyclical, with each generation of stars contributing more heavy elements to the raw material from which the next set of stars will be born. But not in Segue 1 — in contrast to all other galaxies, the new analysis shows that Segue 1's star formation ended at what would ordinarily be an early stage of a galaxy's development. Segue 1 likely failed to progress further because of its unusually tiny size.

"Our work suggests that Segue 1 is the least chemically evolved galaxy known," Simon said. "After the initial few supernova explosions, it appears that only a single generation of new stars were formed, and then for the last 13 billion years the galaxy has not been creating stars."

Because it has stayed in the same state for so long, Segue 1 offers unique information about the conditions in the universe shortly after the Big Bang. Other galaxies have undergone multiple supernova explosions since their formation. The first supernovae to blow up, from the most massive stars, produce elements like magnesium, silicon, and calcium. Later explosions of smaller stars primarily make iron. Segue 1's uniquely low iron abundance relative to other elements shows that its star formation must have stopped before any of the iron-forming supernovae occurred.

Written By: Science Daily
continue to source article at sciencedaily.com

11 COMMENTS

  1. @OP – Other galaxies have undergone multiple supernova explosions since their formation. The first supernovae to blow up, from the most massive stars, produce elements like magnesium, silicon, and calcium. Later explosions of smaller stars primarily make iron. Segue 1′s uniquely low iron abundance relative to other elements shows that its star formation must have stopped before any of the iron-forming supernovae occurred.

    Hence the variation in metalicity in galaxies and sections of merged galaxies, showing the relative proportions of elements available for chemical reactions.

    Heavy elements only exist in areas with a history of supernova explosions of stars which have created heavy elements by nuclear fusion, before exploding the matter back into space.

  2. I checked Stellarium and couldn’t fine Segue 1, so I checked Wikipedia. Converting kpc to light years, it’s only 75k light years away. Kind of like being a paleontologist and finding a family of T. Rex fossils in the university parking lot.

    PS – Stop calling theists “believers” and start calling them “superstionists”. They hate that but can’t argue against it. Please help support this meme.

  3. For some reason, the mention of supernovas remind me of a now defunct science-fiction TV series on NBC called “The Event”. It was based on the idea of this extra-terrestrial civilization that needed to invade the earth because their planet was in a stellar system with a massive star about to go supernova.

    Which brings up a question in my mind…

    Does a massive star live long enough for the dust around it to form planets? If it does, would there be enough time for the process of evolution to lead to intelligent life and civilization, which took billions of years in our case? My personal hunch is no but I’m not an astrophysicist…

    • In reply to #6 by NearlyNakedApe:

      Does a massive star live long enough for the dust around it to form planets?

      It is a feature of massive stars that they form from high concentrations of gas (and dust?) which provides their mass, so there would be plenty of gas (and dust?) in their accretion disks to form planets. The bigger the star, the shorter its life. If the there had been no previous supernova explosions adding to the primordial gas in that area, they may lack the dust of heavy elements. There may be mainly, or only, hydrogen and helium in the “low metalicity” gas cloud, so there may only be gas planets because there are few or no suitable atoms to form rocky planets.

      If it does, would there be enough time for the process of evolution to lead to intelligent life and civilization, which took billions of years in our case? My personal hunch is no but I’m not an astrophysicist…

      That is one of the key contra-indications against finding life orbiting giant stars. I gave an explanation and put a link on this earlier discussion. http://www.richarddawkins.net/news-articles/2014/4/26/traces-of-recent-water-on-mars-liquid-water-on-mars-as-recently-as-200-000-years-ago#comment-box-26

    • In reply to #9 by jax.agnesson:

      I don’t understand how a 13bn y-o galaxy can be ‘nearby’. Shouldn’t it be amongst the most distant objects we can detect? Help?

      Hello,

      I think you may be confusing look back time with age. Segue 1 is about 75,000 light years away means we are seeing it as it was 75,000 years ago. The galaxy is believed to have formed 13 billion years ago. So it has a look back time of 75,000 years and is 13 billion years old.

      Note that if you hold your finger out in front of you at arm’s length the look back time for your finger is about three and a third billionths of a second but your finger is (however old you are) old. Or what makes up your finger is 13.8 billion years old if you’re more liberal about considering it an independent bit of baryons. Now I’m rambling so I’ll stop.

  4. In reply to #7 by Alan4discussion:

    In reply to #6 by NearlyNakedApe:

    Does a massive star live long enough for the dust around it to form planets?

    It is a feature of massive stars that they form from high concentrations of gas (and dust?) which provides their mass, so there would be plenty of gas (and dust?) in their accretion disk… The bigger the star, the shorter its life. If the there had been no previous supernova explosions adding to the primordial gas in that area, they may lack the dust of heavy elements.
    There may be mainly, or only, hydrogen and helium in the “low metalicity” gas cloud, so there may only be gas planets because there are few or no suitable atoms to form rocky planets.

    Or there could be no planets at all , if the lack of heavy elements with their greater gravity, had prevented the atoms and molecules from clumping together strongly enough to resist the forces of a solar wind.

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